During a mode of engine operation commonly known as deceleration fuel shut-off (DFSO), fuel injection to one or more engine cylinders may be interrupted. The DFSO mode is generally initiated when an engine powered vehicle is decelerating, and its engine output control element (throttle valve or accelerator pedal) is positioned for engine idling, i.e. no operator demand for additional engine output. Recovery from the DFSO mode typically occurs, when either the engine rotational speed drops below a predetermined minimum speed near idle, or the engine control element is moved from the idling position to accelerate engine rotation and increase output torque.
The purpose of the DFSO operating mode is to reduce fuel consumption, and provide engine braking that results from frictional drag and negative torque applied to the engine by its load. In engine systems with electronic throttle control (ETC), the position of the throttle is adjusted based on a desired air/fuel ratio. Thus, during DFSO, the throttle is typically adjusted to a closed position since fuel is not being injected to the engine. However, closing the throttle limits airflow through the engine, and increases the braking torque on the engine.
However, the inventors herein have recognized potential issues with such systems. As one example, the braking torque exerted on the engine by closing the throttle may cause the engine speed and/or vehicle speed to decrease by more than a desired rate. Thus, excessive deceleration may occur during DFSO by closing the throttle, thereby shortening the DFSO event with a resultant loss in fuel economy gain. Additionally, when exiting DFSO, there may be a lag in the response of the engine to increases in the driver demanded torque as it may take time for the mass airflow through the intake to increase upon opening of the throttle.
In one example, the issues described above may be addressed by a method for controlling a throttle during deceleration fuel shut off mode. In particular an example method may comprise controlling a position of a throttle in an air inlet of an engine propelling a vehicle, in relation to vehicle operator commands, and during a deceleration fuel shut off mode, increasing opening of said throttle independently of said operator commands when speed of said vehicle is or is expected to fall below a desired speed or desired speed trajectory. The method may in some example further comprise decreasing the throttle opening if the vehicle speed rises above the desired speed or desired speed trajectory during the deceleration fuel shut off mode. Additionally or alternatively, the method may comprise closing the throttle upon initiation of the deceleration fuel shut off mode, and then adjusting the position of the throttle away from a closed position in response to the vehicle speed decreasing below a desired speed.
In another representation, a method may comprise controlling position of a throttle, in an air inlet of an engine propelling a vehicle, in relation to vehicle operator commands, and during a deceleration fuel shut off mode, increasing opening of said throttle independently of said operator commands in response to an indication that a catalyst coupled to an exhaust of said engine will saturate with oxygen during said deceleration fuel shut off mode. In some examples, the catalyst may comprise a three way catalyst containing oxygen storage elements such as ceria. In some examples, the method may further comprise estimating an available storage capacity of the catalyst. The method may additionally or alternatively comprise determining whether the catalyst will store enough oxygen during said deceleration fuel shut of mode to reach the storage capacity or a predetermined percentage thereof. When exiting deceleration fuel shut off mode, the method may additionally comprise not injecting fuel to cylinders of said engine when a mass airflow rate in the engine is greater than a desired mass airflow rate, where the mass airflow rate may be determined based on vehicle operator commands and a desired air/fuel ratio.
In this way, over-braking of an engine during DFSO may be reduced and DFSO prolonged to achieve fuel economy savings. Specifically, by opening a throttle valve during DFSO, a braking torque applied to the engine may be reduced, and a vehicle speed may be more closely aligned with a desired speed profile during DFSO. Further by maintaining the position of the throttle in an open position during DFSO, the responsiveness of the engine to increases in driver demanded torque upon exiting DFSO may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.